Shunting of Guns or Parts
The phenomenon of the secondary current bypasses the nugget being formed is called shunting.
Since shunting always reduces the actual welding current, it should be avoided whenever possible. There are two primary sources of shunting. (1) Shunting due to existing spot welds, as shown in Fig. 1.
Fig. 1. Shunting due to existing spot weld
(2) Shunting due to design, as shown in Fig. 2, where shunting inevitably occurs in series welding process.
Fig. 2. Shunting in series welding process
(Source: GM Automotive Welding Handbook)
If the following weld issues occur, it may very well suggest the incorrect electrode dressing:
- Undersized Weld
- Stuck Weld
- Inconsistent Weld Quality
- Nonround Weld
- Poor Class A Appearance
- If the weld spot is very close to existing welds, then shunting may be significant, such as shown in Fig. 1.
- If the process is shunting designed, such as the series welding as in Fig. 2, then shunting may be significant, especially for galvanized steels when the coating may consume a considerable amount of current.
Quality, Workplace Issues, Cost, Downtime, Maintenance, Throughput (cycle time; PPH), are all potentially affected by this condition. Special considerations are noted below:
Quality: a lot of weld quality issues will occur due to shunting: Undersized weld, Stuck weld, Inconsistent weld quality, Brittle weld, Nonround weld, and Poor Class A appearance.
Workplace Issues: shunting of gun or work sheet in certain extreme cases may be hazardous if not being properly prevented.
- The weld position is too close to an existing weld.
- Inappropriate series welding design.